This invention relates to an apparatus and method for cutting a wiring pattern formed on a semiconductor device.
A faulty spot or area may occur on a wiring pattern or a wiring circuit in the manufacture of semiconductor elements having semiconductor circuits including, for example, redundancy circuits. In this case, the problem can be remedied by cutting such a faulty spot or area. In the conventional method, the faulty spot or area is cut by focusing a laser beam on a predetermined portion of the wiring pattern under atomospheric pressure. As shown in FIGS. 1 and 2, for example, a wiring pattern 6 which is formed on an insulating film 4 overlying a semiconductor substrate 2 is covered by a thin insulating film 8. A laser beam B is directed from a laser beam device 9 toward a predetermined spot or area of the wiring pattern where the wiring pattern is to be cut under atomospheric pressure by the heat of the laser beam. However, the conventional method has the following disadvantages.
First, during the cutting of the wiring pattern 6, the spot or area to be cut may heat to a high temperature of about 1,000.degree. to 2,000.degree. C. As a result, there is a high possibility that ion atoms or ion molecules such as Na.sup.+ will be liberated, causing them to be diffused into an area between the insulating films 4 and 8. Since the ion atoms or ion molecules are mobilized between the insulating films 4 and 8, a variation in the characteristic of the circuit occurs during the operation of the circuit, thus seriously affecting the operation of the circuit.
Second, during the cutting of the wiring pattern 6, only a portion of the pattern 6 is subjected to heating, melting and vaporization. As a result, a portion 8A of the insulating film 8 flies apart, as shown in FIG. 2, by the pressure of the vaporization. The portion of the wiring pattern cannot be vaporized from the molten phase until the insulating film portion 8A flies apart. Since the portion of the wiring pattern which is molten due to the high temperature involved contacts the underlying insulating film 2 for a relatively long time period, a crack 2A may occur or the underlying insulating film 2 may melt, affecting the neighboring P-N junction.
Third, the insulating films which surround the wiring pattern 6 have a thermal diffusion coefficient of about 0.008 cm.sup.2 /sec. in the case of, for example, an SiO.sub.2 film. The thermal diffusion coefficient of air is about 0.5 cm.sup.2 /sec. Where, as shown in FIG. 3, the wiring pattern 6 is not covered with an overlying insulating film, that is, it is exposed, a greater amount of heat escapes into the air, greatly lowering heat efficiency.